When a person descends underwater, the ambient pressure surrounding the body increases rapidly. This pressure increase causes the volume of air spaces within the body to decrease. Equalization is the action of adding air to these enclosed spaces to match the rising external pressure, preventing them from shrinking. Failing to equalize leads to a pressure imbalance between the body’s interior and the surrounding water. This mechanical stress results in a pressure-related injury known as barotrauma.
The Primary Injury: Middle Ear Barotrauma
The most common consequence of failing to equalize is middle ear barotrauma, often called an ear squeeze. The middle ear is an air-filled cavity separated from the external ear canal by the tympanic membrane, or eardrum. It connects to the back of the throat via the Eustachian tube, which is the pathway for air to equalize the pressure.
During descent, increasing water pressure pushes inward on the eardrum because air cannot enter the middle ear through a blocked Eustachian tube. This creates negative pressure inside the middle ear space. The eardrum bulges inward, causing discomfort that quickly escalates into sharp pain as the pressure differential increases.
If the diver continues to descend, the negative pressure pulls fluid and blood into the middle ear cavity, potentially leading to a hemorrhage behind the eardrum. In severe cases, the pressure difference can cause the eardrum to rupture, often accompanied by a sudden feeling of relief as the pressure equalizes. Inner ear barotrauma is a more serious risk if a diver attempts forceful equalization against a blocked tube. This can transmit excessive pressure to the inner ear’s fluid-filled chambers, potentially rupturing the round or oval window and causing sudden vertigo or permanent hearing loss.
Pressure Effects on Other Body Cavities
Barotrauma can also affect other air-filled spaces in the head, including the sinuses and teeth. Sinus barotrauma, or sinus squeeze, occurs when the narrow passages connecting the sinuses to the nasal cavity become blocked, often due to congestion or inflammation. As the diver descends, the air trapped in the sinuses cannot be replenished, creating negative pressure that pulls on the sinus lining.
This vacuum effect causes the mucous membranes lining the sinuses to swell and the blood vessels within them to rupture. The resulting hemorrhage fills the sinus cavity with blood until the internal pressure stabilizes, which relieves the sharp facial pain. This damage may result in a bloody discharge from the nose or post-nasal drip after the dive.
A less common but painful injury is dental barotrauma, or barodontalgia, which affects teeth containing trapped air spaces. This usually occurs in teeth with faulty or old dental restorations, such as crowns, fillings, or recent root canal work. On ascent, the compressed air begins to expand and cannot escape due to the poor seal of the restoration. The expanding air exerts pressure on the surrounding tooth structure, causing severe pain or potentially fracturing the tooth or dislodging the filling.
Recovery and Prevention
If a diver experiences pain or discomfort in the ears or sinuses during descent, the immediate action is to stop descending and ascend slightly until the discomfort subsides. This minor ascent reduces the ambient pressure, making equalization easier. The diver should then attempt to equalize gently before resuming descent slowly. If equalization is impossible, the dive must be aborted to prevent serious injury.
Recovery time depends on the severity of the barotrauma. Mild middle ear barotrauma may resolve in a few days or weeks. A ruptured eardrum requires six to eight weeks to heal spontaneously, and recovery can take several months.
Sinus barotrauma can also take a month or more to fully resolve if swelling is significant. Diving must be avoided until the ability to equalize is fully restored. Medical attention is necessary if symptoms like persistent pain, hearing loss, vertigo, or discharge from the ear are present. Prevention involves avoiding diving when congested, descending slowly, and equalizing early and often before any pressure is felt.